A brief cognitive-behavioral treatment intervention that included an interoceptive exposure (IE) component was previously demonstrated effective in decreasing fear of anxiety-related sensations in high anxiety-sensitive (AS) women (see Watt, Stewart, Birch, & Bernier, 2006). The present process-based study explored the specific role of the IE component, consisting of 10 minutes of physical exercise (i.e., running) completed on 10 separate occasions, in explaining intervention efficacy. Affective and cognitive reactions and objective physiological reactivity to the running, recorded after each IE trial, were initially higher in the 20 high-AS participants relative to the 28 low-AS participants and decreased over IE trials in high-AS but not in low-AS participants. In contrast, self-reported somatic reactions, which were initially greater in the high-AS participants, decreased equally in both AS groups over IE trials. Findings were consistent with the theorized cognitive and/or habituation pathways to decreased AS.